The unknown is Uo (the overall heat transfer coefficient), and here I must agree with you. Where Ntu is the number of transfer units. The effectiveness is no estimate, in fact it can be derived directly from the LMTD method. This kinds of calculation always depend on some empirical formulas. how to get the value of 'e'? it is based on many factors such as tube material, flow configuration etc. I regard this method just be suitable to estimate, not the exact calculation. If you would like to read it, I will send you a link privately (apparently you get suspended by ANDY if you post links) I have published an article on this subject that can be read on my web site. Hswi = enthalpy of saturated air at suction temp. On the other hand, the effectiveness method does not suffer from this problem since Qmax can easily by defined in terms of the enthalpy difference. This means 2-phase heat transfer and so the temperature difference is not the driving force (the driving force in this case is the enthalpy difference). Where the LMTD method fails, is on cooling coils where you have condensation. The LMTD method is good for selectors where the temperatures are specified and you need to calculate the coil size. If you know the leaving temperature of any of the fluids then you have the answer. Seems simple on the face of it but the LMTD demands the knowledge of both fluid leaving temperatures. I'm not fan of LMTD because it requires iteration.

They are theoretically equivalent, so you can use either. There are 2 heat exchanger solve methods: The South African Institute of Refrigeration and Air Conditioning (SAIRAC), has a technical data CD that will cost you about $100. There is a very good book that is available for free download by Prof Lienhard at MIT. This is standard textbook stuff, you will find it in Holman or any other heat transfer text book. Implies that heat lost from hot fluid = heat gain by cold fluid. Note that Q is the same in each equation. Heat transfer from hot fluid to cold fluid.

There are 3 simultaneous equations to solve.ġ. Reason is that there is no iteration so is ideal for hand calculation. The same basic principles apply to all heat exchangers.īest is the e-Ntu method.

Coolpack refrigeration utilité